1. Field of the Invention
The present invention relates to a network interface having at least one of a disconnect mode and a suspend mode in addition to an active mode.
2. Description of the Related Art
An IEEE1394 bus system is standardized as a high speed bus system. The IEEE1394 bus system is a serial bus system in which electrical devices with an interface board in conformity with the IEEE1394. a standard are connected by a standard cable in conformity with the IEEE1394 standard (which will be simply called an IEEE cable). A twisted pair cable is adopted as the IEEE cable, in which the twisted pair cable includes two pairs of two twisted wires in which differential signal is transmitted.
In addition to an active mode, a disconnect mode and a suspend mode are defined in the IEEE board. The active mode is a mode established when information such as packet data is sent/received between nodes. The disconnect mode is a mode established when an opposite node is not connected. The suspend mode is a mode in which nodes are connected but packet data is not sent/received between the nodes.
The active mode and the suspend mode are established by a PHY chip in the IEEE board. The PHY chip includes a cable I/F and a digital control part for processing a signal output from the cable I/F.
The cable I/F in the IEEE board outputs send/receive data to the digital control part. In addition, the cable I/F outputs various signals including a connect detection signal and a bias detection signal, in which the connect detection signal enters an asserted state (becomes Low) when an opposite node is connected, and the bias detection signal enters an asserted state (becomes High) when packet data is sent/received.
The digital control part establishes the disconnect mode, the suspend mode and the active mode according to a value of the connect detection signal and the bias detection signal. More specifically, the disconnect mode is established when the connect detection signal is in a negate state, so that functions are disabled except for the function for executing a mode change process according to change of the connect detection signal.
The digital control part establishes the suspend mode when the connect detection signal is changed to the assert state while the bias detection signal is in the negate state, so that functions are disabled except for the function for executing a mode changing process for the change of the connect detection signal and the bias detection signal. In the suspend mode, when the connect detection signal is changed to the negate state, the mode is changed to the disconnect mode. When the bias detection signal is changed to the assert state, the mode is changed to the active mode, so that functions are enabled except for the function for processing the connect detection signal.
The suspend mode provided in the interface board in conformity with the standard of the IEEE1394.a is a mode provided for decreasing power consumed by each IEEE board when information such as packet data is not exchanged between electronic apparatuses connected by the IEEE cables.
However, while the IEEE board is placed in the suspend mode, a clock signal generation part in the PHY chip continues to operate. In the PHY chip, high speed data processing is performed at a rate of 400 Mbps at the maximum. Therefore, the clock signal generation circuit generates a clock signal with very high frequency, in which a large amount of power is consumed for generating the high frequency clock signal.
It can be considered to stop the operation of the clock signal generation part for power saving. However, if the operation of the clock signal generation part is stopped in the suspend mode, all of the signal processing functions in the PHY chip including a process of the connect detection signal detected in the cable I/F are disabled. Thus, for example, the changing process from the suspend mode to the disconnect mode can not be performed even when the electronic apparatus is disconnected from the IEEE cable. In addition, the IEEE board can not detect information such as packet data sent from a connected electronic apparatus, so that there occurs a problem in that the mode can not be changed to the active mode. When the IEEE board is in the disconnect mode, the same problem occurs if the clock signal generation part is disabled.